The field of the invention is camera dollies and camera pedestals.
In the production of motion pictures, the motion picture camera must often be moved from one position to another. The camera movements may require a change in camera position, camera angle, or camera elevation. The camera movement must be performed smoothly, as even small amounts of vibration of the camera can result in unsatisfactory filming, due to shaky or erratic recorded images. For certain film sequences, the camera must be held in a fixed position. In other film sequences, the camera must be continuously and rapidly moved to follow an action or moving sequence. Similar requirements must often be met when using television cameras.
Camera dollies and pedestals have long been used to support and move motion picture cameras. Typically, a camera dolly has four wheels or pairs of wheels on a chassis having a generally rectangular wheel base. The wheels may be attached to the chassis via articulated legs, or the wheels may be directly pivotably attached to the chassis.
The camera dolly is pushed over the floor by dolly operators. During filming on sand, grass, or other uneven surfaces, the dolly may be placed on rails or tracks to provide an even and smooth rolling surface. The dolly wheels may be adapted for both ground and track operation, or separate ground and track wheels may be supplied as accessories, to be installed, on the dolly as needed. Larger camera dollies may be self-propelled using electric motors and on-board batteries. Camera pedestals provide similar functions and are used primarily in television studios.
Most camera dollies and pedestals are provided with an arm or telescoping column, to raise and lower the camera. The arm maybe a beam arm, or a hinged holding arm. The arm or column is driven hydraulically, pneumatically or electrically. Various accessories, such as pan heads, tilt heads, risers, extensions, remote control camera heads, etc. may be used to move and position the camera as needed. Seats are often attached to camera dollies to accommodate the cameraman. Push bars and handles may be installed to make it easier to push or carry a camera dolly.
Many camera dollies have steering systems which steer the wheels of the dolly, similar to an automobile. A steering bar or handle at the back end of the dolly is turned by the dolly operator to steer the dolly wheels, typically using a series of chains or belts and sprockets contained within the dolly chassis. The camera is normally mounted towards the front end of the dolly.
For added versatility, the camera dolly should be capable of both xe2x80x9cconventionalxe2x80x9d steering and xe2x80x9ccrabxe2x80x9d steering. Conventional or corrective steering refers to a steering mode where the front wheels of the dolly are locked in to a straight ahead position, while the rear wheels of the dolly are controlled by the steering system and are steered at corrected or adjusted steering angles (or vice versa). This mode may also be referred to as 2-wheel corrective steering. As the dolly turns and travels along a curved path, the inside wheel travels on a radius less than that of the outside wheel, as the outside wheel is spaced apart further from the center of the curved path than the inside wheel. As a result, for proper steering, the inside wheel must turn more sharply than the outside wheel.
A similar requirement is found in automobiles, which have steering linkages which attempt to provide corrective steering. However, in automobiles, the corrective steering is not precise. As a result, when automobiles make sharp turns, the tires may scrub somewhat over the payment. The scrubbing generates the screeching or skidding sounds often heard as an automobile makes a sharp turn, even at a low speed. The scrubbing results because each front wheel is not precisely turned to the correct steering angle needed for the automobile to travel on the curved path. However, in automobiles, this small amount of tire scrubbing during sharp turns is acceptable.
In contrast to automobiles, scrubbing and screeching tires are entirely unacceptable for camera dollies. Camera dolly operation must be silent to avoid interfering with the soundtrack of the motion picture or television production, where even an intermittent or relatively low level of equipment noise will be disruptive and unacceptable. Tire scrubbing also makes a camera dolly more difficult to push, due to increased rolling friction. Many camera dollies accordingly have included steering angle correctors or transmissions, for example, as described in U.S. Pat. No. 4,003,584, or 5,174,593.
In these camera dollies, more precise steering angle correction is provided for the conventional steering mode, using cams, moving offset plates, or other mechanical devices intended to achieve correct geometrical steering. That is, these types of steering angle correctors cause the rear wheels of the dolly to more closely track the perfect geometric steering pattern defined by the specific tread width and wheel base of the dolly and a specific turning radius. The front wheels, which are locked into the straight ahead position, do not participate in steering (in the conventional steering mode) and do not need any steering angle correction (similar to the rear wheels of an automobile). The conventional steering mode is often used to simply relocate or position the dolly. Conventional steering mode also is used, for example, when multiple panning or camera turning shots are needed. These types of filming shots might occur during an action sequence where the subject is moving through a hallway having curves or turns.
As is well known in the camera dolly field, to achieve perfect steering geometry in conventional steering mode, the rear wheels must be oriented so that their axes of rotation intersect at a point on a line passing through the center lines of the front wheels. Deviation from these steering angles causes the tires to scrub, if even only slightly, rather than rolling freely. This principle is illustrated in FIG. 47A where X and Y are the rear wheels of the dolly, and K and L indicate the tread and wheelbase respectively, and is explained in detail in U.S. Pat. No. 5,174,593, incorporated herein by reference.
Most camera dollies are also capable of crab steering, which is a steering mode where all wheels of the dolly are steered to the same angle. The crab steering mode, which is commonly used more often than the conventional steering mode, allows the dolly to move forward or back, left or right, or at any angle, as shown in FIG. 44, without changing the xe2x80x9cazimuthxe2x80x9d camera angle of the camera, or the angular position of the dolly. Accordingly, the crab steering mode offers great versatility. When the subject being filmed is distant from the camera lens, the dolly may be shifted laterally, using the crab steering mode, without significantly affecting the camera angle.
In crab steering mode, no steering angle correction is needed or provided. All of the wheels are coupled via chains or belts to the steering bar or handle, and all of the wheels turn together. The wheel rotation axes of all the wheels always remain parallel to each other. The steering angle of each wheel is identical and tracks the steering angle of the steering handle or bar. A shift mechanism is provided to shift between crab and conventional steering modes, depending on the needs of the camera movement sequence. In existing dollies, shifting between steering modes is achieved through movement of a lever, a shift pedal, or other device.
Some camera dollies also provide a round steering mode. In the round steering mode, all of the dolly wheels are turned by the steering system. The front and rear wheels along each: side of the dolly are turned in equal, but opposite direction, as shown in FIGS. 43 and 47B. The wheel rotation axis of all the wheels intersect at approximately a common point located on a lateral center line of the dolly. This allows the dolly to rotate about its geometric center or another point on the lateral center line. Round steering allows the dolly to be turned around in a very tight space as the dolly turns within its own length. In contrast, with conventional steering, almost twice as much space would be needed to turn the dolly around. Round steering must also be xe2x80x9ccorrectivexe2x80x9d in that for proper round steering, the wheel angles must be adjusted to compensate for the steering geometry of the dolly.
While certain camera dollies have previously provided conventional, crab and round steering modes, these dollies generally required multiple operator movements to shift between these steering modes. These shifting movements have required the dolly operator to remove at least one hand from the steering bar to shift between modes, thereby making it difficult or impossible for the dolly operator to continuously and accurately move and steer the dolly, while simultaneously shifting between shifting modes. As split second timing is often required during filming or taping, to appropriately move and position the camera, even the short delay in moving a hand from the steering bar, to a shift lever, can be a significant disadvantage. In addition, unless the operator is highly experienced, the operator will have to look down to locate the shift lever. The operator is therefor unable to continuously watch the dolly, or look for cues, marked floor positions, etc. As a result, dolly operation can be difficult.
In addition, the steering systems in virtually all camera dollies which provide steering and shifting between steering modes, are integrally built in to the dolly, and can be replaced or modified only with substantial difficulty. Accordingly, when a steering system is damaged or otherwise requires service, the dolly becomes unavailable for use until the service or repair can be made.
Accordingly, there remains a need for an improved camera dolly, and for a camera dolly having an improved steering system.
To these ends, a camera dolly includes a camera steering unit which provides for shifting between corrective or conventional steering, crab steering, and round steering, without the operator removing the hands from the steering bar. Preferably, the steering unit has a first transmission and a second transmission linked together for simultaneously shifting between conventional, crab and round steering modes. A differential advantageously has sprockets, which move to offset positions for conventional and round steering. Chains or belts extend around sprockets on the transmissions and differential, and directly or indirectly to the wheels of the dolly. The first and second transmission and the differential, along with other components form a conventional mode steering system, a crab mode steering system, and a round steering system, each selectable with a single handle movement. Linkages preferably control shifting of the components of the differential, and also control movement of dynamic idlers, to maintain appropriate chain tension or belt tension. The camera dolly may be quickly and easily shifted between steering modes with both of the operator""s hands remaining on the steering bar, and without the need for the operator to look or feel for a shifting lever.